To accomplish sterilization methods different sterilants and sterilizers are used. Sterilants and sterilizers are the physical compounds used in the sterilization process (e.g., steam, plasma gas, and ethylene oxide). As compared to traditional disinfectants and antiseptics which kill specific microorganisms (e.g., bacteria and viruses), sterilizers kill all microorganisms and spores to prevent any infections from arising after its use on a patient.   

 

There are multiple sterilization methods: traditional, liquid chemical, medical sterilization, and ethylene oxide (EO) sterilization. 

• Traditional sterilization often involves “thermal methods, such as steam, to achieve sterilization.”  

• Liquid chemical sterilization involves two-parts: 

  1. Devices are treated with a liquid chemical germicide (LCG). 

  2. The processed devices are rinsed with water to remove the chemical residues. 

However, there are limitations for this method. For example, “although the rinse water is treated to minimize any bioburden, it is not sterile. Because the rinse water is not sterile, devices rinsed with this water cannot be assured to be sterile.”  

• Medical sterilization which is classified in three categories: plasma gas sterilization, steam sterilization, and vaporized hydrogen peroxide sterilization.  

  1. Plasma Gas Sterilization: “…low temperature hydrogen peroxide gas plasma within a chamber to kill all living microorganisms on medical and dental equipment, including bacteria, spores, viruses and fungi. 

  2. Steam Sterilization: “…circulates steam at high temperature and pressure to sterilize various items, or as part of an industrial process.” 

  3. Vaporized Hydrogen Peroxide Sterilization: “…vaporized hydrogen peroxide (VHP) sterilization utilizes hydrogen peroxide vapor, but plasma gas isn't used within the process. VHP sterilizers remove humidity from an enclosure and hydrogen peroxide vapor is rapidly injected by a generator to reach an effective concentration to sterilize equipment.  This method has one of the lowest cycle times, resulting in the ability to sterilize equipment in high volume batches.” This method is being frequently used with medical devices containing polypropylene, brass, and polyethylene, due to its efficacy compared to other methods. 

• Ethylene Oxide “Gas” (ETO) Sterilization is sometimes discounted because of the inherent risks. The carcinogenic nature of ETO sterilization emissions has led to the search for alternative sterilization methods and changes to the current EO sterilization method in recent years. These emissions, consisting mostly of chlorofluorocarbons (CFC), lead to damage to the environment as they are known agents of ozone degradation. However, the search for alternatives remains challenging because of thermodynamic and efficacy issues. The efficacy of EO remains the largest in the US, with over 20 billion devices sterilized each year. To date, companies have shown that concentrations at and lower than 300mg/L is lethal enough to kill the Most Resistant Organism (MRO), Bacillus atrophaeus. Changing the EO sterilization concentrations appears to be the most sustainable way to keep this method viable for years to come. The CDC had done extensive research on ETO sterilization techniques including ETO-chlorofluorocarbons (CFC), ETO-carbon dioxide (CO2), and ETO-hydrochlorofluorocarbon (HCFC): 

  1. ETO-CFC 

  2. ETO-CO2: 8.5% ETO and 91.5% CO2 

  3. ETO-HCFC: Both 8.6% ETO and 91.4% HCFC and 10% ETO and 90% HCFC. This is an extremely viable alternative to ETO-CFC as “HCFCs are approximately 50-fold less damaging to the earth’s ozone layer than are CFCs.” 

 

Finding alternatives to traditional ETO-CFC will reduce the need for changes to ISO 10993-7, which measures the residual ethylene oxide on medical devices following this method.

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Since sterilization includes such a wide range of methods it is used by healthcare providers and professionals in almost all medical, laboratory, and cosmetic settings. These methods are often applied in cleanrooms and other sterile sectors of hospitals. Meanwhile, steam autoclaving is a common form of sterilization for lab equipment in research labs. MicroBio consultants work in sterilization techniques for medical devices under FDA and ISO guidance. 

 

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Hospitals, medical and cosmetic practices, and laboratories are the most common places to see sterilization techniques applied. More research is always being conducted to find safer ways to sterilize products with the highest efficacy possible, which could make sterilization techniques more widely applicable. For example, work has been done to provide these sterilization methods in public/cosmetic operations, such as that used for tattoos.  

 

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Sterilization continues to be developed and changed in accordance with FDA, ISO, and environmental guidelines. The development of sterilization methods will continue to improve the maximum sterility for a wide array of devices. MicroBio Consulting works to study and identify the efficacy of rising forms of sterilization, such as EO sterilization, and their application in medical device testing. Using ISO 10993-7:2008 Biological evaluation of medical devices – Part 7: Ethylene oxide sterilization residuals, MicroBio determines whether residual ethylene oxide levels on a medical device is acceptable. Furthermore, in accordance with different FDA and ISO guidelines, MicroBio Consulting also provides guidance for the certification of sterilants and sterilizers. ISO guidelines include ISO 25424:2018 (Sterilization of health care products — Low temperature steam and formaldehyde — Requirements for development, validation and routine control of a sterilization process for medical devices) and ISO11737-2:2009 (Sterilization of medical devices — Microbiological methods — Part 2: Tests of sterility performed in the definition, validation and maintenance of a sterilization process), to ensure the efficacy of sterilization techniques as they are applied to medical devices. (6)